Abstract
The composition and structure of anodic oxides about 400Å thick grown in either 3% tartaric acid/propylene glycol or 
electrolytes are investigated. The ion sputtering effects are taken into account to obtain quantitative chemical depth profiles. The 
oxide is inhomogeneous with an average Ga3+/(oxidized As) ratio of ∼3 and ∼1 in the surface region and the bulk of this oxide, respectively, while the tartaric acid‐grown oxide is homogeneous with a Ga3+/As3+ ratio of ∼1 throughout the oxide film except in the interfacial region. In the outer layer (∼100Å) of the 
oxide, a large quantity of oxygen exists and the arsenic oxide is not 
but 
. In both ∼400Å thick anodic 
interfacial regions, whose width is ∼100Å, excess As exists and its quantity is approximately equal to the concentration difference between 
and 
in this region.